Influence of barrier material and structure on carrier quantum confinement in GaAsBi quantum wells (QWs) is studied comprehensively. Single- and multi-QW structures were grown using solid-state molecular beam epitaxy with conventional rectangular, step-like and parabolically graded AlGaAs barrier designs. It was discovered that room temperature photoluminescence is increased by more than 50 times in the GaAsBi QWs with parabolically graded barriers (PGBs) if compared to standard rectangular and step-like structures. The enhancement of photoluminescence was reproducible within the range of growth parameters. The carrier localization and increase of trapping efficiency in GaAsBi QWs is responsible for observed enhancement in radiative properties of PGB structures. The random potential field fluctuations for carriers were increased up to 44 meV due to the blurred well-barrier interface causing the conditions for Bi content and/or well width variations. Due to the impact of self-organizing effects on the reproducibility of optical properties, the GaAsBi QWs with AlGaAs PGBs open the window for fabrication of 1.0-1.55 μm wavelength emission lasers based on GaAsBi quantum structures.

The dilute bismide alloy GaAs_1-xBi_x has drawn significant attention from researchers interested in its fundamental properties and the potential for infrared optoelectronics applications. To extend the study of bismides, molecular-beam heteroepitaxy of nominally 1.0 eV bandgap bismide on Ge substrates is comprehensively investigated. Analysis of atomic-resolution anti-phase domain (APD) images in the direct-epitaxy revealed a high-density of Ga vacancies and a reduced Bi content at their boundaries. This likely played a key role in the preferential dissolution of Bi atoms from the APD interiors and Bi spiking in Ge during thermal annealing. Introduction of GaAs buffer on offcut Ge largely suppressed the formation of APDs, producing high-quality bismide with single-variant CuPt_B-type ordered domains as large as 200 nm. Atomic-resolution X-ray imaging showed that 2-dimensional Bi-rich (111) planes contain up to x = 9% Bi. The anomalously early onset of localization found in the temperature-dependent photoluminescence suggests enhanced interactions among Bi states, as compared to non-ordered samples. Growth of large-domain single-variant ordered GaAs_1-xBi_x films provides new prospects for detailed analysis of the structural modulation effects and may allow to further tailor properties of this alloy for optoelectronic applications.

We present a detailed study on the optical properties of GaAsBi/GaAs multiple quantum well structure, optimized for the active area for vertical-external-cavity surface-emitting lasers. The quantum structure was grown by molecular beam epitaxy with every other barrier made thinner to have a homogeneous structure with high photoluminescence (PL) intensity. PL measurements were carried out in a wide temperature range from 4 to 300 K. The PL band of 1.085 eV was attributed to the optical transition in QWs with 8.0%Bi. The S-shaped temperature dependence of PL peak positions showed high localization effect of 30 meV. The internal quantum efficiency (IQE) was evaluated for the bismide structures with a modified ABB* method, which includes contribution from trap-assisted Auger recombination. The calculations showed low IQE of <0.025% for GaAs0.92Bi0.08/GaAs 12 QWs structure, which was explained by the low growth temperature, resulting in a high density of point defects in the material.

A set of single quantum well (SQW) samples of GaAs1-xBix with x ~ 0.1 and p-doped GaAs barriers grown by molecular beam epitaxy was investigated by the temperature-dependent photoluminescence (PL) spectroscopy. Those GaAsBi SQW structures showed a high crystalline quality, a smooth surface and sharp interfaces between the layers and exhibited a high PL intensity and a lower than 100 meV PL linewidth of QW structures. Temperature dependence of the optical transition energy was S-shape-free for all investigated structures and it was weaker than that of GaAs. An analysis of the carrier recombination mechanism was also carried out indicating that the radiative recombination is dominant even at room temperature. Moreover, numerical calculations revealed that a higher Be doping concentration leads to an increased overlap of the electron and heavy hole wave functions and determines a higher PL intensity.

Fabry–Perot laser diodes based on (Al, Ga)As and Ga(As, Bi) with single or multiple parabolic or rectangular-shaped quantum wells (QWs) emitting at the 780–1100 nm spectral range were fabricated and investigated for optimization of the laser QW design and composition of QWs. The laser structures were grown using the molecular beam epitaxy (MBE) technique on the n-type GaAs(100) substrate. The photolithography process was performed to fabricate edge-emitting laser bars of 5 μm by 500 μm in size. The temperature-dependent power-current measurements showed that the characteristic threshold current of the fabricated LDs was in the 60–120 mA range. Light and current characteristics were almost linear up to (1.2–2.0) I_th. Low-frequency 10 Hz–20 kHz electrical and optical noise characteristics were measured in the temperature range from 70 K to 290 K and showed that the low-frequency optical and electrical noise spectra are comprised of 1/f and Lorentzian-type components. The positive cross-correlation between optical and electrical fluctuations was observed.